Basic thermoplastics have several critical property disadvantages which limit their use in structural and engineering applications. These deficiencies include cold flow under load, high coefficient of thermal expansion, high temperature use limitations, and generally low strength properties. The use of reinforcing fibers to improve these deficiencies has been technically demonstrated in most thermoplastics. The composite materials have improved strength, temperature resistance, dimensional stability, and rigidity.
The ability of these materials to be fabricated by injection molding at rates equivalent to non-reinforced plastics coupled with improvements in critical engineering properties has not only placed these materials in a position to displace their non-reinforced counterparts in many applications, but also to compete for markets now held by thermosets, non-ferrous metals, and certain alloys.
The mechanism for effective reinforcement of thermoplastics by high strength fibers is based on the transfer and equal distribution of the applied stress from the resin to the high strength fiber reinforcement. Intimate contact of the resin and fiber, through chemical bonding or physical attraction, is essential. Secondarily, uniform distribution of the fiber into the resin matrix must be accomplished with minimum destruction of the fiber.
Glass fibers are generally used to reinforce thermoplastics because of their relatively low cost, availability, and high strength properties. The glass fibers are usually treated with coupling agents (silanes or chrome complexes) which are thought to form chemical bridges between resin and glass, binders to maintain strand integrity and protect the glass during handling, and in some cases anti-static agents.
While most properties of thermoplastics reinforced with glass fibers are improved, some properties, particularly impact strength and deflection temperature, are highly dependent on the chacteristics of the unreinforced thermoplastic involved. Improvements in tensile and flexural strengths, rigidity, and dimensional stability are directly proportional to fiberglass content.